Automatic oven air balancing system



5 Sheets-Sheet 1 Jan. 1, 1963 D. JA, LOWE AUTOMATIC ovEN AIR BALANc-INGSYSTEM Filed Dc. 11, 1957 ATTORNEYS Jan. l, 1963 D. J. LOWE 3,070,897

l AUTOMATIC OVEN AIR BALANCING SYSTEM Filed Dec. 11, 1957 5 Sheets-Sheet2 I OPEN e e G I No VOLATILES I i e e e e e g i Pm'lAl.voLrlLEJcoNDITIoN g i INVENTOR. DONALD J. Lowa ATTORNEYS D. J. LOWEAUTOMATIC OVEN AIR BALANCING SYSTEM Jan. 1, 1963 5 Sheets-Sheet 5 IFiled Dec. 11, 1957 INVENTOR. DONALD J. LOWE ATTORNEYS Jan. 1, 1963 D.J. LowE AUTOMATIC OVEN AIR BALANCING SYSTEM 5 Sheets-Sheet 4 Filedv Dec. 1l, 195'?" T INVENTOR. DQNALD` J. |.owl-2l ATTORNEYS Jan. l, 1963 D.J. LowE 3,070,897

AUTOMATIC OVEN AIR BALNCING SYSTEM Filed' Dec. ll, 1957 5 Sheets-Sheet 5j E l z s 3k z i Eig-B i I e s f# i I L i N A H 3g INVENTOR.

DONALD J. LOWE BY United States Patent O 3,070,897 AUTOMATIC OVEN AIRBALANCING SYSTEM Donald J. Lowe, Northfield Center, Ohio, assgnor tYoung Brothers Company, Cleveland, Ohio, a corporation of Michigan FiledDec. 11, 1957, Ser. No. 702,120 Claims. (Cl. 34-46) This inventionrelates to automatic control of the exhaust in an industrial oven of atype in which heated air is caused to ow over the work and at least aportion of such airis desirably recovered for recirculation.

The eiciency and economy of operation of such an oven is obviouslyaffected by .the volume of warm air coming from the work which may thusbe re-used, with of course due regard to the moisture content of therecovered air and, in many cases, to the character of the entrainedvapor and gases where the process carried out involves more than thesimple extraction of water from the work. For example, resinous coatingsapplied to tin plates are baked in metal decorating ovens and suchcoatings usually comprise volatile solvents driven olf in the heatingand resulting in a flammable exhaust. Safety specifications require thatthe atmosphere in such an oven :be maintained below a particular levelof concentration of the volatile gas and, accordingly, the considerationof recirculation for maximum economy is limited in this respect, as Wellas by the usual effect of the moisture content on the efficiency ofdrying.

The amount of air which is exhausted is known as the exhaust overlapand, in ovens designed for treating decorated metal particularly, theprior practice has .been to size the exhaust overlap to satisfy thevolatile gas concentration limit for the maximum solvent load which maybe encountered in the oven. Accordingly, more make-up air than is neededis taken in during operation at lesser loads, with a correspondingexcess in the fuel consumed as compared yto operation with that exhaustand recirculation condition actually effective to provide a safe andproper atmosphere for the particular load being handled.

It is accordingly a primary object of my invention to provide a variableexhaust system forrsuch an oven in which a .portion of the ow from thework is variably divided between recirculation and exhaust automaticallyin accordance with regulation of the fresh air supply and venting of theoven, whereby oven balance or pres-v sure can be maintained with thedegree of recirculation controlled to afford the most economical andefficient condition thereof.

Another object is to provide such a variable exhaust control, includingautomatically regulated recirculation, in which the system is responsiveto the presence and concentration of combustible matter in the ovenatmosphere and effective to hold the level thereof below a predeterminedsafe limit.

It is also an object of the invention to provide practical and reliablestructure constituting an oven control characterized by the operationalfeatures noted in `the above.

Other objects and advantages of the present invention will becomeapparent as the following description proceeds.

To the accomplishment of the lforegoing and related ends, the invention,then, comprisesthe features hereinafter fully described and particularlypointed out inv the claims, the following description and the annexeddrawings setting forth in detail certain illustrative emq bodiments ofthe invention, these being indicative, however, of but a few of thevarious ways in which the principle of the invention may be employed.

Patented Jan. 1, 1963 ICC In said annexed drawings:

FIG. l is a side elevational view, partly in section, of the firstoperative zone of a continuous conveyor oven equipped with control meansin accordance with the present invention;

FIG. 2 is a transverse sectional view taken on the plane of the line 2-2in FIG. l;

FIG. 3 is a semi-diagrammatic view illustrating the major components ofsuch system;

FIG. 4 is a table which illustrates diagrammatically various conditionsof adjustment of the system;

FIG. 5 is a fragmentary elevational view showing the control means usedwith the exhaust damper of the system;

FIG. 6 is a sectional view taken on the plane of the line 6-6 in FIG. 5;

FIG. 7 is a further section taken along the line 7-7 in FIG. 6; and

FIG. 8 is a wiring diagram showing the electric circuits used forautomatic control of the system operation.

Referring now to the drawings in detail, the metal decorating oven shownpartially in FIG. 1-conventionally comprises a .tunnel housing 1 throughwhich an endless wicket-type conveyor, designated generally at 2 anddriven by electric motor 3, carries the tin plates for baking of thecoatings thereon. Since the volatile solvents in such coatings aredriven off in the iirst heating zone 4 of the oven, and my new controlis concerned with exhaust of the same, only this initial zone has beenillustrated, the sheets or plates being loaded on the wickets at theright end and being moved through the oven in the direction of thearrow. For obvious convenience and clarity, the conveyor is not fullyshown.

The source of heat for this zone is a burner S in which by an electricmotor 9, connected to the shaft 10 thereof through a belt 11, andpropels the heated air -from the burner downwardly through a supply boot12 which extends along the outer side of the oven housing to a At 'isuch region, the boot is connected to a distributor pan region below theupper course of the conveyor.

13 in the oven which is longitudinally enlarged and bridged transverselyat its upper periphery by a number of cross pieces 14 in spaced apartparallel relation. The

separation of such pieces of course forms transverse slots through whichlthe heated air currents are discharged' from the pan or manifold forflow upwardly through the conveyor bearing the metal sheets and henceacross the coated surfaces of the latter. I

A recirculatin'g duct 15 of inverted U-shape, as shown most clearly inFIG. 2, extends along the top portion of the oven heating chamber from apoint adjacent the end wall 16, above the entrance hood 17, to a pointbeneath the burner 5 where it terminates in a slightly enlarged open endsection 18. Adjacent the end wall 16, the duct is provided with a topopening 19 and above the same the oven has a vertical extension 20leading to an exhaust Ablower 21. The latter is driven by an electricmotor 22 through a belt drive 23 to the shaft 24 of the same and createsa forced draft upwardly through a suitable stack, a portion of which isshown at 25.

As indicated, such oven construction is generally conventional and itwill be understood that there are successive heating zones for carryingout the complete baking process. The recirculating duct 15 does notextend over the complete length of the .lower supply manifold 13 butterminates short of the inner end of the latter, whereby the aircurrents discharged over a predetermined extent at this end areordinarily unimpeded in return flow to the burner 5.` Such flow must.proceed through a series of transverse ports 26 above the conveyorwhich yare adjustable by virtue of being defined by slide members 27..Over the remaining, and greater, length of this first heating zone theair proceeding from the work ows into the rie-circulating duct throughslots formed by longitudinally spaced apart cross members I28 bridgingthe open bottom of the duct. Such members are hollow, for a purpose tobe described.

In order to provide a variable exhaust, this oven is equipped with anexhaust damper 29 in its vertical end portion 20 and a fresh air damper30 in the intake 6 of the burner, these two dampers of course beingintended to vary the intake and exhaust in relation to one another. Tomaintain proper pressure or balance in the oven with such variableexhaust, I provide a plurality of overlap dampers 31-36, respectively,in the recirculating duct 15, ywith the damper 31 of such series beingAlocated at and adapted to close the inner end 18 of the duct beneaththe burner chamber and the other dampers spaced longitudinally along theduct and capable, when moved to vertical closed condition, of variablydividing the same longitudinally to regulate the exhaust overlap or thedivision of the air flow from the duct between the burner and theexhaust stack 25. The effective length of the duct is determined by thedampers 31, at one end, and 36, at the other end. I have shown six suchoverlap dampers, but it will be understood that this number can bevaried as required to meet best particular conditions of operation .anddimensions of the oven.

For convenience of illustration, the fresh air damper 30 is shown in theschematic diagram of FIG. 3 on a horizontal shaft so as to correspondwith the other control dampers which are actually pivoted on horizontalaxes. The damper arrangement shown in FIGS. l and 3 and in block A ofthe FIG. 4 table is thus the same and provides one condition ofoperation wherein the intake and exhaust dampers are fully open, theinnermost overlap damper 31 is closed, and theremaining overlap dampers32-36 are open. In such condition, it will be clear that. all the airflowing into the recirculating duct 15 from the work is exhausted, i.e.,that there is maximum exhaust overlap. Block B of the FIG. 4 tableillustrates the damper positions at the opposite lim'it, for maximumrecirculation, with the intake and exhaust dampers being completelyclosed, overlap damper` 36 at the otherA end of the recirculating ductclosed,` and the remaining overlap dampers 31-35 open. Block C ofthetable illustratesan intermediate condition in which thevintake andexhaust dampers are partially and cor- 4respondingly open, overlapdamper 34 is closed, and they In this last noted` other overlap dampersare open. intermediate condition, the closed overlapv damper 34 forms alongitudinal divider in the duct 15, with the air entering the same atthe right of such damper being exhausted and air in the duct to the leftof the damper being returned to the burner 5 for recirculation. Otherintermediate conditions are established by closing dif-v ferent ones ofthe overlap dampers to vary such longitudinal division and henceproportioning of the air coming from the work lbetween exhaust andrecirculation.

By properly relating the division effected by the over-1 lap dampers tothe settings of the intake and exhaust dampers, maximum recirculationpermissible for safe and eicient operation can be had with differentloads in the oven. Operation of the system is desirably automatic and inthe preferred embodiment of the invention, the concentration of volatilegas in the exhaust is used as the condition to which the systemoperation responds.

In such embodiment,l the fresh air damper 30 is op.

erated by a proportional air motor 37, such as a Taylor lever motor,adapted to be connected to a controlled air -supply through a three-waysolenoid air valve AVI (c g. an Asco valve) operative as a safetydev-ice in a manner to be described hereinbelow, said valve having aninlet 38 for connection to the air supply of the motor 37 and an exhaust39. Exhaust damper 29 is .moved by a similar air motor 40 preferablyconnected to the same controlled source as motor 37, a further safetyvalve AVZ included in like association with the motor 40. rPhe overlapdampers are actuated by spning-return air cylinders il-d6 controlled bysolenoid operated air valves AV4-AV9, with the usual supply and exhaustconnections. The air cylinders t1-46 and air valves AV4-AV9 areconstructed and operate in identical manner, the air cylinder 46 and theair valve AVlt being cross sectioned in FIG. 8 for illustrativepurposes. The air cylinders and air valves are conventional and form nopart of the instant invention. Referring briefly to FIG. 8 it will beseen that when the solenoid actuated valve AV4- is deenergized, thesupply inlet to said valve is closed whereby damper 36 is under thecontrol of the spring in the air cylinder 46. When the solenoid in valveAV4 is energized, the inlet port is uncovered thereby allowing thepressurized air to flow through said valve into the bottom of the aircylinder 46, thus rotating the damper .36. The intake and exhaustdampers 29 and 30, respectively, are thus proportionally adjustable bytheir air motors, whereas the overlap dampers operate between full openand closed positions. With regard to the overlap dampers, the spring ofcylinder 41 holds damper-3l normally closed and the other such dampersare spring-biased open by their respective operating cylinders.

Operation of the overlap dampers can be made dependent on the setting ofeither of the exhaust and fresh air dampers, and I have illustrated anarrangement whereby movement of the former determines such operation. Asshown in FIGS. 5 to 7, the shaft 47 on which the exhaust damper 29 ismounted projects through a bearing 48 held in the rear wall 49 of abox-like housing 50 secured to the outer wall 51 of the oven, the shaftextending through this housing and outwardly thereof being connected tothe arm 52 of the air motor 40 supported on such wall by a bracket 53.Within the housing 50, a cam plate 54 is fixed onthe shaft and a seriesof limit switches Sl-SS are mounted on brackets 55 holding the actuatorsof these switches adjacent the periphery of the cam plate. The latter isdivided into quadrants at alternating radii, whereby there are tworaised cam surfaces 56 diametrically opposite and each approximately inextent; the remaining intermediatedepressed surfaces 57 provide loss ofcontact between the plate and the switch actuators. Switch S2 is spacedwith its actuator 120 from top center, switch S4 at 150, switch S1 at285, switch S3 at 315, and switch S5 at 345. The cam is here shown inits position corresponding to the exhaust damper 29 in its normal fullopen position and it will be clear that turning of the damper causesactuation of the switches individually in sequence.

The movement of the intake and exhaust dampers is controlled by anexhaust gas analyzer and control assembly of commercially availabletype, such as made by Davis Instruments, such assembly being operativeto measure the combustibility of the exhaust gas, and to provide asignal proportional to the volatile gas or vapor present. The analyzerand control assembly includes an analyzer which isindicated in thewiring diagram of FIG. 8 by reference numeral 58, the same beingconnected between conductors L1 and L2 of an ordinary 1l() volt supplythrough a manual switch 59. The usual alarm horn 60 for emergencycondition, also provided by Davis Instruments, is shown connectedthroughA a normally open switch 61 and an interlock relay R is connectedbetween L1 and L2 through switch 59 and through a normally closed switch62.

The analyzer and control assembly supplied by Davis Instruments alsoincludes a detector D, over which gas is passed and burned on a platinumwire, the temperature thereof being measured by a thermocouple T toprovide the control signal. The detector unit D of the analyzer assemblyis preferably located in an appropriate location in the oven to samplethe atmosphere in the same, for example, in the exhaust extension 20 asshown in FIG. l. The control signal from the thermocouple T is appliedto a proportioning potentiometer-type pneumatic controller M, alsosupplied by Davis Instruments and forming part of the analyzer andcontrol assembly. This controller is connected, as shown, in the supplyline 38 to the air motors 37 and 40, the branched outlet from thecontroller leading to the two valves AV1 and AV2. The controller M iswell known in the art and comprises a pressure regulating valve which isresponsive to the control signal produced by the thermocouple T. Thepressure regulating valve regulates the pressure of air supplied to themotors 37 and 40 through supply line 38. Such regulation results in avariable positioning of dampers 30 and 29, respectively, such variablepositioning depending as will be apparent, on the pressure of the airsupplied to the motors 37 and 40. As clearly set forth above, theanalyzer and control assembly is commercially obtainable from DavisInstruments and thus forms no part of the instant invention. I haveaccordingly indicated such conventional structure in FIG. 8 by enclosingthe same within a dotted line enclosure.

As will be understood, when the combustible gas in the exhaustincreases, the analyzer 58, detector D, and thermocouple T will respondto such increase by way of changing the control signal to the controllerM whereby the pressure regulating valve therein effects a decrease inthe pressure of air flowing therethrough, thus moving dampers 29 and 30toward fully open position.

The safety valves AV1 and AV2 serve only as safety devices and function,in the event of an electric power failure, to cause the air motors 37and 40, respectively, to move the dampers 30 and 29 to their full openposition whereby gas is completely exhausted from the system. There isthus provided a fail safe feature which insures the exhausting of allgases in the event of power failure, thereby eliminating the possibilityof ignition of any combustible gases. It should also be noted that, asset forth above, the springs of the overlap damper cylinders 41 to 46,in the non-actuated condition of such cylinders move these dampers tothe positions shown in FIG. 3, so thatv maximum exhaust overlap obtainsupon failure of the power supply. During normal operation of the system,i.e., in the presence of a power supply, the supply of air ows directlythrough valves AVI and AV2 to the motors 37 and 40 respectively, thelatter valves not affecting theA tiow in any manner. Under suchconditions, the air supply to the air motors 37 and 40 is under thecontrol of' the regulating valve of controller M, which functions asexplained above. Referring to the operation of valves AV4-AV9, of whichvalve AV4 has been selected for illustrative purposes l(FIG. 8), whenvalve AV4 is in a deenergized state, the' piston rod and heads movedownwardly due to gravity, the downward movement being cushioned by thespring mounted in the bottom of the cylinder, whereby the supply line38' is closed and the exhaust line 39 open. When the solenoid isactuated, the pistons in the cylinder of AV4 move upwardly therebyclosing the exhaust line and opening the supply line. Air is thussupplied to the bottom of the piston in cylinder 46 thereby forcing thepiston rod upwardly, thereby pivoting damper 36 about its stationary,horizontal axis and closing said damper. When valve AV4 is deenergized,the spring in cylinder 46 will force the air below the piston outwardlyof the cylinder 46 and through the exhaust line in valve AV4.

, The Valves AV4-AV9 which control the several overlap dampers areconnected in parallel between the supply lines L1 and L2 through themain manual switch 59 and the several limit switches S1-S5. Each limitswitch, except switch S1, as illustrated in FIG. 8, is operative in twoof the valve circuits simultaneously to open one and close the other.Switch S1 is either opened or closed in both the branch circuits ofvalves AV4 and AVS simultaneously.

In the open position of dampers 32-36 and closed position of damper 31,whereat full exhaust occurs, switch S1 is closed in the branch circuitsof control valve AV4 and control valve AVS; switch S2 is closed in thecircuit of valve AVS, and open in the circuit of control valve AV6;switches S3 and S4 are similarly arranged and operative in thesucceeding valve circuits, being open in one circuit and closed inanother. The last switch S5 during full exhaust is closed in the circuitof valve AV8 and open in the circuit of control valve AV9. Suchoverlapping connections provide sequential operation of the dampers in amanner to be described.

When the main switch 59 is moved to on position, this position beingshown in the FIG. 8 diagram, and the analyzer does not detect anycombustible gas in the exhaust, the controller M causes the motors 37and 40 to move the inlet and exhaust dampers 30 and 29, respectively, tofully closed position. The damper 29, in moving from a fully open to afully closed position, rotates in a counterclockwise direction about itshorizontal axis, as depicted in FIG. 3. This counterclockwise rotation,shown by the solid line arrow in FIG. 3, will close, in sequence,switches S5, S4, S3, S2 and S1 through raised cam surfaces 56 of camplate S4, referring to FIG. 6. At the end of the counterclockwiserotation of damper 29, the overlap damper 31 will be open and the damper36 will be closed, through energization of valves AV9 and AV4,respectively, and the dampers 32-35 will be in their open position, thevalves AV8, AV7, AV6 and AVS, respectively, having been first energizedand then deenergized during the 90 counterclockwise rotative movement ofdamper 29. This fully closed condition of dampers 29 and 30 isillustrated in block B of FIG. 4. When dampers 29 and 30 are fullyclosed the entire amount of the exhaust gas is recirculated.

It will be understood that if the analyzer and control assembly detectsan excess of volatiles in the exhaust before the dampers 29 and 30 reachtheir fully closed position, controller M will cause the dampers 29 and30, through the air motors 37 and 40, and, more specifically, throughthe pressure regulating valve in controller M, to remain in a partiallyand variably open position as long as the excess volatiles are presentin the exhaust, such a partially open position being shown in FIG. 4C.As shown therein, when the dampers 29 and 30 are in a partially openposition, one of the intermediate overlap dampers will be cosed, damper34 in block C of FIG. 4 being shown in such closed position. It will beapparent that the particular intermediate damper in closed position willdepend upon the degree of rotation of damper 29, as shown in FIG. 3. Theclosing of damper 34 indicates that damper 29, and cam plate 54operatively connected thereto, will have rotated to a position whereincam surface 56 has closed switch S2 in the branch circuit of valve AV6thereby energizing valve AV6. In this partially open position of dampers29 and 30 it will be understood that a portion of the exhaust gas iscaused to recirculate subsequent to combination thereof with fresh air,and the remaining portion of the exhaust gas is exhausted.

If, after the damper 29 has reached a closed position whereby maximumrecirculation is effected, the analyzer and control assembly senses anexcess of volatiles in the recirculated air, the controller M, which isresponsive to the thermocouple T, moves dampers 29 and 30 to a partiallyopen position, in a clockwise direction as shown by the dotted linearrow in FIG. 3, thereby exhausting a portion of the air entering thecirculation duct 15 and diluting with fresh air the remaining,recirculated air portion, as explained above. Movement of the dampers 29and 30, through the air motors 40 and 37, respectively, via thecontroller M, as stated above, is in a clockwise direction from theirclosed position. As the damper 29 rotates in a clockwise direction, theswitches S1, S2, S3, S4 and S5, in sequence and in that order, come outof contact with the raised cam surfaces 56, as will be apparent fromFIG. 6, such clockwise movement being shown therein by a dotted, curvedarrow line. Thus, when switch S1 comes out of contact with cam surface56, the circuit through control valve AV4 is closed thereby returningthe damper 36 to its horizontal position. The closing of switch S1 alsocompletes the branch circuit through the control valve AVS whereby thesame is energized to move the overlap damper 35 to a closed position,whereby a portion of the air entering the recirculating duct isexhausted. When switch SZ is opened, damper 35 assumes its open,horizontal position and damper 34 becomes closed, whereby a greaterproportion of air entering the recirculating duct is exhausted. Theoperation proceeds in this manner until the maximum exhaust condition isreached. At maximum exhaust, as will be understood, the exhaust gas iscompletely exhausted from the system and fresh air is supplied to saidsystem through the air inlet opening 6. It will be understood that ifthe proper volatile content of the air can be obtained with partialexhaust and partial dilution with fresh air, the damper 29 will notreach the vertical, bock A, full exhaust FIG. 4 position but will assumethe block C, FIG. 4 position and remain there until the volatile contentof the air either increases or decreases, whereupon controller M willcause the air motors 37 and 40 to correspondingly move the dampers 30and 29, respectively, in the proper direct'on to achieve optimumrecirculation and exhaust conditions.

It is preferable that the oven Ibe provided with means precludingcondensation of vapor on the surfaces of the recirculating ductassembly, and for such purpose, the duct walls are spaced from the ovenwalls as `shown in FIG. 2. Heated air can thereby circulate about theouter surface of the duct to prevent condensation of solvent in theexhaust thereon. Furthermore, the hollow cross members 2S are connectedat their ends to two longitudinally extending side ducts ed and have aseries of apertures 65 along the tops of the same. Duets 64 areconnected through conduits 66 to an auxiliary gas burner 67 (FIG. 1) forcirculation of heated air currents through the cross pieces, and twofurther ducts 68 lead from the burner 67 to the space betweenthe ovenand recirculating duct near the work-entering endof. the roven wheremaximum solvent evaporation takes place, it being clear from FIG. 2 thatthe topand side walls of the recirculating duct are spaced inwardly ofthe oven.

It will accordingly be seen that the construction illustrated anddescribed provides return of a relatively fixed, but adjustable, amountof the ow proceeding from the work zone to the furnace or heat source atthe inner end of the same where there is in normal operation negligibleevaporation of volatile matter. Likewise independent of therecirculating ductjmeans, a certain amount of the flow is exhausted atthe work entrance end, the high evaporation area, under control of theexhaust damper. The latter and the fresh air damper are thus regulableto establish various exhaust settings for the oven.

The remaining major portion of the ow leaving the work enters therecirculating duct means to afford control over the same, i.e., in thedivision thereof between the burner 5 and the exhaust, and such controlis tied to the regulation of the oven exhaust setting. In such manner,the system provides a variable exhaust with automatically relatedvariation in the degree of recirculation to maintain balance of the ovenair, and by making the exhaust adjustment responsive to thecombustibility of the oven gases, as disclosed, it is possible to meetall safety requirements of the nature discussed without excessiveexhaust E overlap and without the excess consumption of fuel resultingfrom the same.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims or the equivalent of suchbe employed.

I, therefore, particularly point out and distinctly claim as myinvention:

l. An oven comprising walls defining a work-receiving chamber, means fordischarging heated air in a lower por.- tion of said chamber for owupwardly therethrough, a collector duct in an upper portion of thechamber having top and side walls in spaced relation to the chamberWalls, whereby oven air is free to circulate about said duct, the bottomof the duct being partially closed by a series of transversely extendingmembers spaced-apart to form inlets for the entry of air to the duct,said members being hollow, a source of heated air currents, and conduitmeans connecting said. members to said source for flow of heated airthrough the former.

2. An oven as set forth in claim l characterized further in that suchhollow members are provided with apertures for discharge of the heatedair supplied to the same into the collector duct.

3. An oven comprising Walls defining a work-receiving chamber, a heatsource, means for flowing heated air from said heat source upwardlythrough said work-receiving chamber, vent means for exhausting air fromthe chamber, an elongated collector duct means in an upper portion ofsaid chamber and open at the bottom for entry of air thereinto, saidduct means at one end communicating with said heat source and at itsother end with said vent means, barrier means transversely within theduct means intermediate the ends thereof, said barrier means forming atransverse partition in the duct means to divide the ow of said heatedair entering the same between the heat source for recirculation and thevent means for exhaust, and means for adjusting the barrier means tovary the effective longitudinal position of the transverse partitionformed by the same in the duct means, thereby to provide differentdegreesof recirculation and exhaust of the air which enters the ductmeans.

4. An oven as set forth in claim 3 wherein said barrier means comprisesa series of dampers in longitudinally spacedrelation within the ductmeans, said dampers being selectively movable by said barrier adjustingmeans lfrom a horizontal open position to a vertical closed position andreturn so that only one damper at any time is vertical, thel othersbeing horizontal, whereby the flow of air entering the duct means isdivided between recirculation and exhaust.

5. An oven comprising walls defining a work-receiving chamber, aheatsource, an adjustable fresh air intake for said heat source, means forowing heatedair from said heat source upwardly through saidwork-receiving chamber, adjustable vent means for exhausting air fromthe chamber, collector duct means in an upper portion of.

said chamber and open at the bottom for entry of air thereinto, saidduct means at one end communicating with said heat source and at itsother end with said vent means, regulating means for adjusting saidfresh air intake and said vent means to establish different exhaustsettings for the chamber, barrier means transversely within the ductmeans intermediate the ends thereof, said barrier means 4forming atransverse partition in the duct means -rtoV divide the flow of airentering the same between the heat source for recirculation and the ventmeans for exhaust, barrier-adjusting means for varying the effectivelongitudinal position formed by the barrier means in the duct means,thereby to provide different degrees of recirculation and exhaust of thesaid heated air which enters the duct'means, and control means foroperating said barrier-adjusting means to increase the amount of airproceeding from the `ductmeansto .the vent rneanszwi-thl increase in thecombustible mixture in Ithe exhaust of the chamber.

6. An oven as set forth in claim wherein said barrier means comprises aseries of dampers in longitudinally spaced relation within the ductmeans, said dampers being selectively movable by said barrier adjustingmeans from a horizontal open position to a vertical closed posi- -tionand return so that only one damper at any time is vertical, the othersbeing horizontal.

7. An oven comprising walls defining a work-receiving chamber, a heatsource, means for flowing heated air from said heat source upwardlythrough said work-receiving chamber, means for returning a first portionof the heated air flow through the chamber to the heat source forrecirculation, vent means for exhausting air from the chamber, means fordirecting a second portion of the heated air flow through the chambersubstantially directly to the vent means for exhaust thereof, collectorduct means in an upper portion of the chamber and open at the bottom forentry of the remaining portion of the ow, said duct means at one endcommunicating with said heat source and at its other end with said ventmeans, barrier means transversely within the duct means intermediate theends thereof, said barrier means forming a transverse partition in theduct means to divide said remaining portion of the ow between the heatsource for recirculation and the vent means for exhaust, and means foradjusting Ithe barrier means to vary the effective longitudinal positionof the transverse partition formed by the same in the duct means,thereby to provide different degrees of recirculation and exhaust of theremaining portion of the ow which enters the duct means.

8. An oven comprising walls defining an elongated work-receivingchamber, conveyor means for carrying work longitudinally through saidchamber, a heat source, means for owing heated air from said heat sourceupwardly through the chamber, a vent for exhausting air from thechamber, a duct extending along the interior of the chamber above theconveyor means, said duct being open at the bottom for said heated airflow into the same, with the duct at one end communicating with the heatsource and at its other end with said vent, barrier means within theduct forming a transverse partition in the same, so that said heated airentering the duct at the same side of the barrier means as the end ofthe duct communicating with the heat source proceeds from the duct tosaid source and said heated air entering the duct at the other side ofthe barrier means proceeds to said vent, the flow of air which entersthe duet thereby being divided between recirculation and exhaust, andmeans for adjusting the effective longitudinal position of the barriermeans to vary .the division of the said heated air ow which enters theduct between the heat source and the vent.

9. An oven comprising walls defining an elongated work-receiving chamberhaving an entrance for the work at one end and an exit therefor `at theother end, conveyor means for carrying work longitudinally through thechamber from the entrance to the exit of the same,

a heat source, means for discharging heated air from said source in thechamber beneath the conveyor means for upward How through the chamber, avent for the chamber adjacent the entrance end of the same, a collectorduct extending along the interior of the chamber above the conveyormeans and being open at the bottom for entry of said heated air to thesame, said duct communicating at one of its ends with the heat sourceand at its other end with the vent, means for conducting a portion ofthe upward flow of said heated air adjacent the entrance end of thechamber substantially directly to the vent, means for conducting anotherportion of the upward flow to the heat source from an inner region ofthe chamber independently of the duct, the remaining portion of the flowentering the duct, barrier means in the duct forming a transversepartition therein to divide the duct into first and second longitudinalsections respectively communicating at the duct ends with the vent andthe heat source, and means for shifting the effective longitudinalposition of the barrier means in the duct to vary the relative size ofsaid first and second sections thereof.

10. An oven for the heat treatment of 'work the heating of which causesvolatiles to be released, comprising walls defining a work-receivingchamber, a heat source, means for liowing heating air from said heatsource upwardly through said work-receiving chamber, vent means forexhausting air from the chamber, collector duct means in an upperportion of said chamber and open at the bottom for entry of airthereinto, said duct means at one end communicating with said heatsource and at its other end with said vent means, barrier meanstransversely within the duct means intermediate the ends thereof, saidbarrier means forming a transverse partition in the duct means to dividethe flow of air entering the same between the heat source forrecirculation and the vent means for exhaust, barrier-adjusting meansfor shifting the effective longitudinal position of the barrier means inthe duct means to provide different degrees of recirculation and exhaustof the air which enters the duct means, means for measuring theconcentration of volatiles in the ow through the vent means, and controlmeans responsive to said measuring means for operating thebarrieradjusting means to increase and decrease the exhaust from theduct means respectively with increase and decrease in the thus measuredconcentration of volatiles.

References Cited in the le of this patent UNITED STATES PATENTS1,431,145 Bolling Oct. 10, 1922 1,779,569 Thompson Oct. 28, 19301,779,622 Drelein Oct. 28, 1930 1,888,573 Sadwith Nov. 22, 19322,073,825 Beck et al. Mar. 16, 1937 2,134,906 Byron Nov. 1, 19382,135,512 Holven Nov. 8, 1938 2,671,969 Mayer Mar. 16, 1954 2,850,086Sanscrainte Sept. 2, 1958

5. AN OVEN COMPRISING WALLS DEFINING A WORK-RECEIVING CHAMBER, A HEATSOURCE, AN ADJUSTABLE FRESH AIR INTAKE FOR SAID HEAT SOURCE, MEANS FORFLOWING HEATED AIR FROM SAID HEAT SOURCE UPWARDLY THROUGH SAIDWORK-RECEIVING CHAMBER, ADJUSTABLE VENT MEANS FOR EXHAUSTING AIR FROMTHE CHAMBER, COLLECTOR DUCT MEANS IN AN UPPER PORTION OF SAID CHAMBERAND OPEN AT THE BOTTOM FOR ENTRY OF AIR THEREINTO, SAID DUCT MEANS ATONE END COMMUNICATING WITH SAID HEAT SOURCE AND AT ITS OTHER END WITHSAID VENT MEANS, REGULATING MEANS FOR ADJUSTING SAID FRESH AIR INTAKEAND SAID VENT MEANS TO ESTABLISH DIFFERENT EXHAUST SETTINGS FOR THECHAMBER, BARRIER MEANS TRANSVERSELY WITHIN THE DUCT MEANS INTERMEDIATETHE ENDS THEREOF, SAID BARRIER MEANS FORMING A TRANSVERSE PARTITION INTHE DUCT MEANS TO DIVIDE THE FLOW OF AIR ENTERING THE SAME BETWEEN THEHEAT SOURCE FOR RECIRCULATION AND THE VENT MEANS FOR EXHAUST,BARRIER-ADJUSTING MEANS FOR VARYING THE EFFECTIVE LONGITUDINAL POSITIONFORMED BY THE BARRIER MEANS IN THE DUCT MEANS, THEREBY TO PROVIDEDIFFERENT DEGREES OF RECIRCULATION AND EXHAUST OF THE SAID HEATED AIRWHICH ENTERS THE DUCT MEANS, AND CONTROL MEANS FOR OPERATING SAIDBARRIER-ADJUSTING MEANS TO INCREASE THE AMOUNT OF AIR PROCEEDING FROMTHE DUCT MEANS TO THE VENT MEANS WITH INCREASE IN THE COMBUSTIBLEMIXTURE IN THE EXHAUST OF THE CHAMBER.